With a rapid increase in the use of fossil fuels, there is an increasing demand for use of alternative energy or clean energy. The field of electricity generation and accumulation using an electrochemical reaction has been most actively studied to meet the increasing demand.
As a representative example of electrochemical devices using such electrochemical energy, secondary batteries are currently used and an application area thereof has gradually been increased. Recently, with an increase in development of technology and demand for portable devices, such as portable computers, mobile phones, cameras, and the like, demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, much research on lithium secondary batteries, which have high energy density, high operating potential, a long cycle lifespan, and a low self-discharge rate, has been conducted, and such lithium secondary batteries are commercially available and widely used.
Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. In the secondary battery, lithium ions released from a positive electrode active material are intercalated into a negative electrode active material such as a carbon particle through 1st charging and the lithium ions are deintercalated through discharging. As lithium ions reciprocate between the positive electrode and the negative electrode as such, they transfer energy. Therefore, the secondary battery can be charged and discharged.
Artificial graphite is one of the negative electrode active materials commonly used to improve charging and discharging characteristics of a battery due to its excellent ability to absorb lithium ions. However, artificial graphite has a problem in that cohesion between artificial graphite particles and adhesion between an artificial graphite particle and a current collector are poor.
Korean Unexamined Patent Publication No. 10-2014-0008982 discloses the use of a binder having a specific viscosity and including a copolymer of a hydrophilic monomer and a hydrophobic monomer to improve cohesion and adhesion. However, even when the binder is used, cohesion between artificial graphite particles and adhesion between an artificial graphite particle and a current collector are not sufficiently exhibited because the binder is disposed in a concave portion of a surface of artificial graphite when artificial graphite in the form of a secondary particle with an irregular surface is used.
Therefore, a negative electrode, which sufficiently exhibits cohesion between artificial graphite particles and adhesion between an artificial graphite particle and a current collector even when artificial graphite in the form of a secondary particle with an irregular surface is used, is required.